In the automotive industry, actuators are used for a number of purposes, including in vehicular systems such as power take-off units and drivetrain systems such as differentials, axle disconnect systems, or power transfer units. As just one example, typical all-wheel drive systems for vehicles push torque through a torque coupling to the secondary axle to provide enhancements in performance, handling and mobility. These systems require that the secondary axle, and the rest of the driveline, be continually rotating at road speed, which reduces the overall efficiency of the vehicle, and reduces fuel economy.
Secondary axle disconnects are available and they permit the secondary axle and prop shaft to stop rotating. These disconnect systems increase vehicle efficiency, but the current systems also require power to both engage and disengage the output and/or remain engaged or disengaged. The latter situation may require constant power to the system, which reduces overall system efficiency, or may require the use of permanent magnets.
As is known in the art, the actuator converts electrical current into mechanical force. The flow of electrical current into the actuator creates a magnetic field that moves a metal armature which, via additional mechanical elements, results in a change in the engagement/disengagement status of the particular drivetrain or other vehicular system, such as the axle disconnect system described briefly above.
Traditionally, when the actuator was energized, the armature would be drawn towards the solenoid as a result of the magnetic field generated, engaging the axle disconnect system. If it was desirable to keep the system engaged, either current would have to be continually applied or permanent magnets would have to be included in the design of the actuator so that the armature would stay in the engaged position. For obvious reasons, it is not desirable to have a solenoid draw significant power when holding the system engaged (or disengaged).
Latching solenoids can also accomplish maintained engagement with a permanent magnet in the system. Use of permanent magnets has undesirable consequences such as temperature demagnetization and shock demagnetization. In addition, depending on the material, permanent magnets can be costly, difficult to fasten, and can be fragile.
In a previous invention, filed as U.S. Prov. Appln. Ser. No. 62/023,944 filed Jul. 13, 2014, and PCT Appln. No. PCT/US15/40195 filed Jul. 13, 2015, both of which are hereby incorporated herein to the full extent permitted by law, an actuator was described that takes advantage of the residual magnetism in the coil housing that remains even after power to the solenoid has been shut off. The previous invention uses this residual magnetism to keep the actuator in an engaged position without a continual power draw.
However, in any of the given situations described above, a latching solenoid is unable to tolerate any incidental movement of the plunger. Incidental movement can cause the solenoid to become fully disengaged and will result in a loss of engagement of the system. The latching solenoid would need to be reactivated to correct the accidental disengagement. The invention described herein allows for the plunger to remain engaged while allowing for unintended force to be absorbed before causing disengagement. The particulars of the plungers of the invention can be tuned to suit the application requirements.